ext4: fix ext4_flush_completed_IO wait semantics

BUG #1) All places where we call ext4_flush_completed_IO are broken
    because buffered io and DIO/AIO goes through three stages
    1) submitted io,
    2) completed io (in i_completed_io_list) conversion pended
    3) finished  io (conversion done)
    And by calling ext4_flush_completed_IO we will flush only
    requests which were in (2) stage, which is wrong because:
     1) punch_hole and truncate _must_ wait for all outstanding unwritten io
      regardless to it's state.
     2) fsync and nolock_dio_read should also wait because there is
        a time window between end_page_writeback() and ext4_add_complete_io()
        As result integrity fsync is broken in case of buffered write
        to fallocated region:
        fsync                                      blkdev_completion
	 ->filemap_write_and_wait_range
                                                   ->ext4_end_bio
                                                     ->end_page_writeback
          <-- filemap_write_and_wait_range return
	 ->ext4_flush_completed_IO
   	 sees empty i_completed_io_list but pended
   	 conversion still exist
                                                     ->ext4_add_complete_io

BUG #2) Race window becomes wider due to the 'ext4: completed_io
locking cleanup V4' patch series

This patch make following changes:
1) ext4_flush_completed_io() now first try to flush completed io and when
   wait for any outstanding unwritten io via ext4_unwritten_wait()
2) Rename function to more appropriate name.
3) Assert that all callers of ext4_flush_unwritten_io should hold i_mutex to
   prevent endless wait

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>

1 files changed, 5 insertions, 3 deletions

diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c
index 8d849dae8428..792e388e7b44 100644
--- a/fs/ext4/indirect.c
+++ b/fs/ext4/indirect.c
@@ -807,9 +807,11 @@ ssize_t ext4_ind_direct_IO(int rw, struct kiocb *iocb,
 
 retry:
 	if (rw == READ && ext4_should_dioread_nolock(inode)) {
-		if (unlikely(!list_empty(&ei->i_completed_io_list)))
-			ext4_flush_completed_IO(inode);
-
+		if (unlikely(atomic_read(&EXT4_I(inode)->i_unwritten))) {
+			mutex_lock(&inode->i_mutex);
+			ext4_flush_unwritten_io(inode);
+			mutex_unlock(&inode->i_mutex);
+		}
 		/*
 		 * Nolock dioread optimization may be dynamically disabled
 		 * via ext4_inode_block_unlocked_dio(). Check inode's state